They are all very different, and in different ways.
In a straight line, the M6 will leave the M5 for dead, it's much, much faster. The M6 is also a better motorway mile muncher, not that the M5 is bad, the M6 just makes it effortless.
In the twisties, there is probably not a lot in it, the M6 is heavier but has slightly wider tyres.
Tech wise, the M6 is obviously better, the HUD especially is fantastic as is the surround view (although I wish there was a front camera as there is in the i8), Nav is more modern, the iDrive system has matured and is very easy to use and navigate.
Practicality, the M5 probably just wins, the boot is theoretically slightly smaller, but the opening and shape are more useful. Rear head room in the M6 is slightly less, but leg room more.
Comfort, not much in it. Once the M6 seats are adjusted correctly they are great. The M5 seats are very good to and with less adjustment somehow easier to get right.
The DCT in the M6 is great if you're on a track or in stop start traffic, you can just be lazy and the auto part does a great job. You can get a little more involvement using manual mode, but it still doesn't have the degree of involvement that using a clutch and manual gear lever do. For manoeuvring, especially reverse hill starts the DCT and electric hand brake combination is shit, just bloody hard to control. There is so much power and the way it engages meany you have to almost instantly get the throttle pedal position just right. Not enough and you roll forwards, too much and you wheel spin backwards. Same in snow, the M5 gives much better usable traction.
The steering in the M5 (especially now it's back to normal after changing the servotronic valve) gives much more feedback than the steering in the M6. It feels like there is a lot of rubber between the steering wheel and the track rods in the M6. This dampens vibrations etc. but it also limits feedback so it's relatively numb. The whole experience in the M6 is more 'remote' than the M5, if you had no speedo you could easily be doing 130 in the M6 and think it was 70.
From a visibility point of view, which includes parking and placing the car accurately on a track or down a narrow lane with oncoming traffic the M5 wins hand down. Both are big cars, but the M5 feels much smaller to drive. In the M6 you're lower down, the lowest seat position on the M5 is about the same as the highest on the M6. This makes it more difficult to judge the front of the car. The A pillars are much wider in the M6, they will undoubtedly give better strength but they hamper visibility especially in conjunction with the door mirrors. The combination create a very significant blind spot looking at about 1 to 2 o'clock, just where you need to look to judge the curb. I've never curbed a wheel on the M5, in the first year of owning the M6 I curbed 3, although now I'm more used to it I've not done another since.
The M1, that's a different ball game. It always feels special to drive, not because the interior is plush, it's quite austere, but because of the history of the car and the engine just behind your head. It's about as fast as the M5, probably would corner much better if you pushed it, which I haven't! It's surprisingly easy and comfortable to drive, the possible exception being the tweed like material of the seats which must be one of the best thermal insulators known to man, if it's hot, your back and bum get very warm indeed.
Bottom line, they all feel epic, in their own unique way.
The M6, it looks fantastic and goes like shit of a shovel, there are not many cars you're likely to come across on the roads that could live with it. But at the same time you can drive 300 miles, collect your slightly nervy mother and father-in-law and drive the 300 miles back to be home by lunch time. I did that when they planned to drive up for my sister-in-laws wedding the day before, got a phone call very early in the morning saying they had set off as planned and then lost their bottle, turned round and gone back home. Obviously they had to attend their own daughters wedding, so I just went and got them!
The M5 is probably the most 'normal' car, it does everything very well, but does not excel at anything. It's fast, but not ballistic. It handles well, but would be left for dead by any number of small nimble sports cars. It does not stand out, to many people it's just an old 5 series. It's got a big boot and can seat 5 in comfort. I took my son to University for the first time in it, 5 up and all his crap in the boot, no problem at all, it would have been possible in the M6, but a bit of a squeeze for the occupant of the middle rear seat.
The M1, it's a bloody M1! Every time you go out in it you get looks. Almost every time you fill up at the petrol station someone wants to talk about it, "You don't see many of those about". But I'd really not want to use it as my daily driver. It's the oldest. It has the most character. It needs respect as it has no power steering, no ABS, no traction control, no air bags, no seat belt tensioners. It's raw, but surprisingly civilised, drive from North Yorkshire to Munich, about 1000 miles, in two days, no problem.

When I lived in the UK I always felt that personalised number plates intended to refer to names were very chavvy and a lot were owned by total wankers but occasionally I encountered an amusing plate. My favourite was seen on a Range Rover standing outside the local manor house in Shropshire. The plate FAT 61T had been slightly amended to read FAT GIT.
Luckily here in Portugal we don't have personalised plates and my formerly UK registered car now bears the inoffensive registration 04-84-VM

As it's been more than 6 years since the full respray, looking at the playing card reflections made me think it would be interesting to do the same thing again and compare various parts of the car.
Back in 2011, as all the car had been done at the same time, the finish was very uniform. Since then the boot lid and both front doors have been replaced, the bonnet repainted (twice!) and the bonnet covered in a clear wrap.
So, how do those areas compare with parts of the paint untouched since 2011?
I rummaged through my draws to find the same playing card I'd used in 2011. Unfortunately the weather was not quite so good as when the original pictures were taken, so the car is inside under LED lights rather than outside in the sunshine. First, the areas that have not been touched, the same areas that were pictured previously
The roof
The rear wing
They look pretty much the same, pretty flat, still nice and shiny!
How about the passenger side front door, replaced in June 2013 due to corrosion on the seams.
the boot lid, done at the same time as the passenger door.
or the drivers door, replaced October 2014 due to the same issue as the passenger door
and finally, the bonnet. Repainted both in 2013 and 2014 (in 2014 it was taken back to bare metal again) then covered with clear protective film.
You can definitely see the slight texture of the film, not so much in the reflection of the playing card, but in the reflection of the out of focus bottom edge of the wall cupboards.
Overall though, still a pretty consistent texture and finish. I'm pretty happy with that.

I fully agree with you. It is starting to depress me now.
I watched QuestionTime last night. Every argument which the SNP had, I had one better
i then was dreaming about it this morning. Hopefully I'm too busy this weekend to care about politics.

If you do work it out please rewrite the instructions in understandable English as the translation on that German website is confusing me! Also, what gauge is it that he has in the pic? It's not mpg like we have.
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I occasionally get the horrendous screeching. To describe it, imagine a "Just Married " car where someone has tied a chain of tin cans dragging on the road behind, it sounds like that.
A good Jet Wash poking the lance at the disk/pad area shifts it.
I've no idea how a small stone or some such could create such a noise but it's happened about 4 times over the last 5 years, and is definitely memorable.

@Funknhell to be honest with you I just laugh when I msg guys on other forums or call guys enquiring about coding BMW and get hit with ridiculous bills, or id give you a bespoke deal for £150 lol. I do know its not a major thing as to what I want done as I previously owned an Audi S4 and have VCDS software which I personally did my coding etc. I totally dont know much about BMW at all as my household has always been VAG cars. But ive been digging deep doing my research and this forum seems to be by far a good UK 5 series one.
Id be grateful if you got back to me with some news.
cheers pal!

You know that was my exact response to my colleague who was telling me about his personalised plate, when he was trying to tell me that a 6 was a B and a G was a D. He claimed it was unique and I retorted with "and so is mine or I should £&@/ing hope so!"

Debris between disc and hub gets my vote too. Sometimes even aggressive wire brushing can leave the tiniest speck stuck to the mating surface. I've even used a scraper on occasions.
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"I think they're tolerable if they're not try hard or so contrived as to be laughable. "
That's my view. The better ones are ok-ish (e.g. I used to see M4 MUM around here), but some are pretty cringeworthy. There are loads of Land Rover vehicles around these days, mostly black, tinted windows, 'unique' plates...yawn.
I do already have a unique plate - the standard year-related one. [emoji1]
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Most aren't 'personalised' plates in the sense that they were created by the owner, they just happen to be older 'normal' DVLA issues that fit with someone's initials, business name etc.
But anyway, yes I have two. One of them, K8 LCJ, I bought about eight years ago for £295 - its significance? I call it my 'family plate' K8 = Kate, L = Lauren, C = Cameron, J = Julie, in other words, the kids and wife. I usually have that on my bike, but it's on retention as I'm in-between bikes at the moment.
The other is MD11 FLY . Now, for those of you not into civil aircraft types, the MD-11 was the successor to the DC-10 widebody passenger transport in the 90s and I thought that an aircraft type and 'FLY' as a reg plate was too good to miss, particularly at only £395. I think that DVLA missed a trick there. I've only assigned it once to a vehicle, a bike, but it's been on retention for a few years now. In the past I've been offered four figures for it from a couple of pilot colleagues, so I may just sell it on.
The only thing I think is a bit naff is when people space letters to make a word or name, also using the plate fixing bolts to create a dot or make a C look like and E etc - I saw that the other day. I just think that looks really crap, sorry.

I've watched the SNP since 2004 .... their special welcome to the workers of the world DVD back in 2005 must have been forgotten by the Scottish.
The SNP cares little about Scotland or the Scottish .... Just as the mob in Westminster really cares little about the people of Britain